Transportation in Animals and Plants

Double circulation: Blood passes through the heart TWICE per complete circuit:

1. Pulmonary circulation: Right heart → lungs (picks up O₂, drops CO₂) → left heart
2. Systemic circulation: Left heart → body (delivers O₂, picks up CO₂) → right heart

Heart structure:

• 4 chambers: Right atrium, Right ventricle, Left atrium, Left ventricle
• Right side: Deoxygenated blood (from body → to lungs)
• Left side: Oxygenated blood (from lungs → to body)
• Valves: Prevent backflow; bicuspid (mitral) valve between left atrium and ventricle; tricuspid between right atrium and ventricle; semilunar valves at aorta and pulmonary artery openings
• Heart rate: ~60–100 beats/minute (resting adult); each beat pumps ~70 mL blood

Blood vessels:

• Arteries: Carry blood AWAY from heart; thick, elastic walls; blood under high pressure; no valves; carry oxygenated blood EXCEPT pulmonary artery (carries deoxygenated to lungs)
• Veins: Carry blood TOWARD heart; thinner walls; lower pressure; have valves (prevent backflow); carry deoxygenated blood EXCEPT pulmonary vein (carries oxygenated from lungs)
• Capillaries: Microscopic; single cell layer thick; site of gas/nutrient exchange between blood and cells

Lymph and lymphatic system — the body's drainage and immune network:

What is lymph?

• When blood plasma leaks out of capillaries into surrounding tissue, it becomes tissue fluid (interstitial fluid)
• This tissue fluid enters the lymphatic capillaries → now called lymph
• Lymph is a pale yellowish fluid; similar composition to plasma but with no red blood cells and fewer proteins
• Contains lymphocytes (a type of WBC) — key immune cells

Lymphatic vessels:

• A network of thin-walled vessels (similar to veins, with valves to prevent backflow) running throughout the body
• Collect tissue fluid from around cells → carry it back to blood circulation
• Lymph eventually drains into the subclavian veins (large veins near the heart) — returning fluid to the bloodstream

Lymph nodes:

• Small bean-shaped structures along lymphatic vessels (in neck, armpits, groin, abdomen)
• Filter lymph: trap bacteria, viruses, cancer cells, foreign particles
• Contain dense clusters of lymphocytes → produce antibodies and destroy pathogens
• Swollen lymph nodes = immune system actively fighting infection (common during throat infections, flu)

Functions of the lymphatic system:

1. Drainage: Returns tissue fluid to blood → prevents oedema (swelling from fluid accumulation)
2. Immunity: Produces and circulates lymphocytes; lymph nodes filter pathogens
3. Fat absorption: Lacteals (lymph vessels in small intestine) absorb fats (as chylomicrons) from digested food → carry to bloodstream (fats bypass the liver via this route)

Key distinction:

• Blood circulation = closed (stays in vessels; heart pumps it)
• Lymph circulation = open (tissue fluid seeps into lymph capillaries; no pump — moved by muscle contractions and breathing)

How blood clots (haemostasis):

When a blood vessel is injured, three overlapping steps occur:

Step 1 — Vascular spasm: Damaged vessel walls contract immediately → reduces blood flow to the area.

Step 2 — Platelet plug formation:

• Damaged vessel wall exposes collagen fibres beneath the endothelium
• Platelets (thrombocytes) stick to collagen and to each other → aggregate into a platelet plug
• Platelets release chemical signals (ADP, thromboxane A2) → attract more platelets → plug grows
• This is fast (seconds to minutes) — provides immediate but temporary seal

Step 3 — Fibrin clot (coagulation cascade):

• Platelets and damaged tissues release thromboplastin (also called tissue factor)
• Thromboplastin (in presence of Ca²⁺ ions and Vitamin K) → triggers a cascade:
  • Prothrombin (inactive; in plasma) → Thrombin (active enzyme)
  • Thrombin converts Fibrinogen (soluble plasma protein) → Fibrin (insoluble threads)
• Fibrin threads form a mesh over the platelet plug → traps RBCs → hard, stable clot (scab)

Why this matters for UPSC:

• Vitamin K deficiency → impaired clotting → excessive bleeding (Warfarin is a Vitamin K antagonist used as blood thinner in heart patients)
• Haemophilia: Genetic disorder (X-linked); clotting factor VIII (Haemophilia A) or IX (B) absent → blood doesn't clot → severe bleeding risk
• Dengue fever: Platelet count drops drastically → impaired clot formation → haemorrhagic dengue; platelet transfusion may be required
• Aspirin: Inhibits platelet aggregation (Step 2) → used to prevent heart attacks (blood clots in coronary arteries)

Xylem and phloem:

Xylem (water transport):

• Transport of water from roots to leaves (upward) through dead, hollow xylem cells
• Why water goes up (against gravity):
  1. Root pressure: Roots actively absorb water from soil → pushes water up
  2. Transpiration pull (main mechanism): Water evaporates from leaf stomata → creates tension/suction that pulls water up the entire height of the tree
  3. Capillary action: Adhesion + cohesion of water molecules in narrow xylem vessels

A tall tree can transport water 100+ metres upward — entirely through passive mechanisms (no pump)

Phloem (food transport):

• Transports sugars (sucrose produced by photosynthesis) from leaves to all other parts
• Bidirectional: Can move sugars up (to growing shoot tips) or down (to roots, fruits)
• Active transport (requires energy — ATP)

Transpiration:

• Water loss from plant through stomata (leaves) and lenticels (stems)
• Benefits: Creates the pull that moves water up xylem; cools the plant (like sweating)
• 98% of water absorbed by roots is lost through transpiration (only 2% used in photosynthesis)
• Transpiration is how forests create their own rain (water released → condenses → precipitation); deforestation disrupts this cycle → less rainfall in the area

ABO Blood Group System:

Discovery: Karl Landsteiner discovered the ABO system in 1901 (initially typing A, B, and C — C later renamed O). AB type discovered by Decastello and Sturli in 1902. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for this discovery — it transformed surgery and emergency medicine worldwide.

The four blood groups:

Rh factor (Rhesus factor):

• A separate antigen (D antigen) on RBC surface — either present (Rh+, "positive") or absent (Rh−, "negative")
• Creates 8 blood types in total: A+, A−, B+, B−, AB+, AB−, O+, O−

Universal donor and recipient:

• O-negative (O−): Universal donor for red blood cells — has no A, B, or Rh antigens; safe to give to anyone in emergency when blood type unknown; only ~6% of India's population is Rh-negative (rarer than globally where O− is ~7%)
• AB-positive (AB+): Universal recipient — accepts all blood types; ~7.74% of India's population (multicentric study, PMC)

Blood group distribution in India:

• O: ~37% (most common)
• B: ~32%
• A: ~23%
• AB: ~8%
• Rh-positive: ~94%; Rh-negative: ~6% (India has lower Rh-negative prevalence than Europe/Americas)

Why compatibility matters: If mismatched blood is transfused, the recipient's antibodies attack donor RBCs → haemolytic transfusion reaction → clumping (agglutination), vessel blockage, kidney failure → can be fatal. This is why blood is typed and cross-matched before every transfusion.

India's updated blood collection data:

• India collected approximately 14.6 million units (2024-25) — near numerical sufficiency nationally
• Requirement: ~14.6 million units/year
• However, ~20-25% still comes from replacement/family donors (not voluntary) — quality risk since replacement donors may conceal infections due to social pressure
• NBTC (National Blood Transfusion Council, 1996): Apex policy body; target = 100% voluntary blood donation
• Regional maldistribution: Rural and tier-2/3 cities face shortfalls even when aggregate numbers appear sufficient